NA 11 - Basal Ganglia PDF

Pag. 1 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia Neuroan#13 – 26/11/2021 Basal ganglia Basal ganglia: controlling, selecting, behaving, timing, planning...Th...

Pag. 1 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia Neuroan#13 – 26/11/2021 Basal ganglia Basal ganglia: controlling, selecting, behaving, timing, planning...The controversial one. Prof. Dellavia – 26/11/21 – Author: Gabriel Pozzan – Reviser: Kussai Chama IMPORTANT. During the lesson, Professor Dellavia said some sentences that in my opinion didn’t make much sense. I wrote them the exact way she said them, but I couldn’t elaborate myself to make it clearer, therefore the portions that I consider not being clear are in red, in order to leave you the choice to either remove them or to keep them. Note also that Professor Dellavia stated multiple times (I also asked her for confirmation), that the substantia nigra has the input (receival of information) at the level of the substantia reticularis and the output (deliver processed information) from the pars compacta. This statement does not parallel neither what the book nor what Professor Cerri explained to us. Basal ganglia are nuclei located at the base of the forebrain. They are positioned deep inside the white matter of the 2 hemisphere. Basal nuclei are anatomically divided in: corpus striatum, amygdaloid body and claustrum. Corpus striatum is related to the motor system, the other 2 have completely different roles. Corpus striatum is a complex of nuclei involved in the regulation of movements under the voluntary control. It plays an important role in the planning of movement (preparation of the motor act), indeed, when learning a new movement, the corpus striatum is involved to prepare the function in order to be memorised and so to be repeated properly. The corpus striatum can be subdivided in: Caudate nucleus. Lentiform – it is subdivided in globus pallidus and putamen. The amygdaloid body (amygdala) is a complex of nuclei subdivided in 2 major system. It is part of the limbic system, this involves part of the limbic lobe (gyri in the cortex of the limbic lobe) and other structures such as part of the reticular formation, hypothalamus, part of the thalamus and part of the amygdala. The Claustrum is a nucleus with a non-completely understood function. It is thought to be a complex relay nucleus involved in superior functions, hence it integrates many typology of signals, including in particular visual information. Circuits and actual function of the claustrum are not yet known. 1. Anatomical locations and relationships Lateral to the putamen is a thin layer of white matter called external capsule, proceeding laterally is the claustrum and then another thin layer of white matter separating the claustrum from the insular lobe (cortex), the extreme capsule. The insular lobe has a cortex made by short and long gyri being very deep inside and not completely visible because of the opercle. Due to the location of the claustrum, it is thought to have relations with the insular lobe. The image shows a frontal view of a coronal section.  Pag. 2 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia The tail of the caudate turns inferiorly around the lentiform and so running below the putamen in order to move anteriorly, and resulting located anteroinferior with respect to the lentiform, it is therefore visible in a coronal section immediately below the head of the caudate. Amygdaloid body and claustrum are anatomically linked to the corpus striatum. The amygdala is a spherical structure being connected on one side to the tail of the caudate nucleus and to a formation of white matter, the fornix. The fornix has 2 columns anteriorly and 2 limbs posteriorly, it connects the mammillary body of the hypothalamus to the amygdala. The thalamus is medial to the corpus striatum. By superimposing the 2 of them on a lateral view, and by observing the position of the lentiform and the thalamus, it is possible to notice that the lentiform is slightly anterior with respect to the thalamus. Therefore, in an anteroposterior direction the corpus striatum is more extended with respect to the thalamus, this can only be appreciated on the posterior aspect of the lentiform. [Author’s note: In the image a horizontal section is seen to see the orientation. The thalami are not only organised from anterior to posterior but also from medial to lateral posteriorly, which is not exactly what occurs for the lentiform.]  Pag. 3 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia In this horizontal section the internal capsule can be seen, being larger than the extreme and the external capsule. The internal capsule is a crucial white matter structure for the passage of information: all of the projections (ascending and descending system), the correlation system and the reverberant circuit to the cortex (circuits involving the basal ganglia). It is V shaped, characterised by a short anterior limb, a genu and a longer posterior limb: The anterior limb is inbetween the head of the caudate and the putamen. The posterior limb is inbetween the putamen and the thalamus. The genu is inbetween the head of the caudate and the anterior portion of the thalamus. Additional limbs are present that can be appreciated from other views. Posteriorly the internal capsule continues with a retrolentiform limb starting from the posterior aspect of the thalamus and the lentiform, then moves posteriorly. Indeed this contains the optic radiation directed towards the calcarine fissure to reach the primary visual cortex.  Pag. 4 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia A horizontal section seen from a superior view. Corpus callosum and thalamus are seen. Lentiform nucleus is not visible, just the head of the caudate.  Pag. 5 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia 1. Amygdala It is a spherical structure, can be divided in 2 main groups of nuclei. Corticomedial. It is the more external portion and the medial part. This is in continuation with a portion of the limbic system called the uncus. The corticomedial region is dedicated to the olfactory information, indeed it is connected with the olfactory bulb through afferent fibres passing into the uncus. Ventrolateral. It represents the rest of the amygdala is formed by the central portion and the basolateral region, being properly components of the limbic system, therefore involved in its functions: processing of emotions, visceral system (fight-or-flight response), sexual pleasure and memorisation (storage of data).  Pag. 6 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia 2. Limbic system Inside the limbic system are complex of white and grey matter. Limbic system is involved in: Control of emotional status and of the corresponding behaviour (somatic and visceral reaction) Connections of the unconscious information (managed in specific areas such as the hypothalamus) at the conscious level (for which the thalamus has a role). Short-term storage of memory. Components of the limbic system located in the: Telencephalon o Cortical areas – limbic lobe (dentate, parahippocampal and cingulate gyri). o Nuclei – hippocampus and amygdaloid body. o Tracts – fornix. Diencephalon o Thalamus – the 3 anterior nuclei. o Hypothalamus – connected to the anterior part of the thalamus, to the 3 homologous nuclei anteriorly, involved to manage emotions and the control of visceral functions (homeostasis). Brainstem o Reticular formation.  Pag. 7 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia Several regions are connected to the limbic systems for which it provides an output. The system is also involved in the control of the vegetative response through the descending pathways. Indeed from the reticular formation fibres targeting the beta motoneurons in the spinal cord are present (from raphe magnus and locus coeruleus), aimed in regulating the peripherical autonomic system (visceral response modulation). The system receives afferent feedback signals from the target organs. 3. Corpus striatum Caudate nucleus and putamen are referred to as the neostriatum. The anterior portion establishing a connection between the 2 of them forms the nucleus accumbens, being the recent phylogenetically acquired (recall the name ‘neo’). The globus pallidus is the inner medial portion of the corpus striatum, it can be divided in an internal and external portion. It is the first that has developed, therefore called paleostriatum. The 2 of them are functionally different. The neostriatum is the input (receives information), the globus pallidus represents the output (delivers information). Th main afferents (inputs) fibres are received from: The cerebral cortex, mainly from the ipsilateral one and from all areas, even though most of the information comes from specific areas (SM). Basal ganglia are indeed involved in the reverberant circuit to the cortex: receive information from the cortex and feeds it back. The intralaminar thalamic nuclei, the corpus striatum can though also send fibres to the intralaminar nuclei of the thalamus (double way course). Substantia nigra, again it can send afferents but can also receive fibres from the corpus striatum. These afferents are a large bundle. Substantia nigra is a nucleus of the midbrain even though it is not exactly possible to have a a clear distinctive division between the 2 as it is a continuous structure.  Pag. 8 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia The main efferent (output) fibres are sent to: The thalamus in order to be projected back to the cortex. Different nuclei are involved: - nonspecific nuclei, the intralaminar mainly but also the centromedian. - 2 specific nuclei (VA, ventral anterior and VL, ventrolateral), meaning that specific areas of the cortex are fed back. The subthalamus, which can give back to the corpus striatum, even if it is mainly the corpus striatum that sends information to the subthalamus that then gives off fibres to the thalamus, from which the cortex is reached. In the image the main structures involved in the circuit are shown. The corpus striatum receives mainly from the motor areas of the cortex, but also from the sensory. From the globus pallidus of the corpus striatum an output to the thalamus is provided to then communicate with the cortex. Corpus striatum can receive directly from some nuclei of the cortex and from the substantia nigra. A flux of information comes also from the brainstem, this can then be integrated at the level of the thalamus and in the corpus striatum through the serotonin pathway. The output is represented mainly by the inner, medial and small portion of the lentiform nucleus, which is the globus pallidus internus. The fibres going out of the corpus striatum are therefore also called the pallidofugal fibres, these have to pass across the white matter of the internal capsule. There are different possibilities, on the way for reaching the thalamus (either specific or nonspecific nuclei), some structures can be found that the fibres have to turn around: The subthalamus, if the fibres do not stop there, has to be bypassed forming 2 different tracts, passing either: - Superiorly – fasciculus lenticularis. It passes superiorly to the subthalamus to then pass medially and inferiorly turning around an additional structure located inbetween the thalamus and the subthalamus, called uncertain zone (unknown group of neurons under study -> seems to be involved in the control of pain). - Inferiorly – forming the Ansa reticularis. The fibres pass in the inferior portion of the internal capsule moving then medially it is possible to curve and reach the thalamus. In general other white matter structure can be turned around along the course. By passing either inferior to the subthalamus or superiorly and then moving more medially, the column of the fornix can be turned around, to then go up and enter in the thalamus. NST: subthalamic nucleus. CM: intralaminar thalamic nuclei. Vla/VA: ventral lateral and ventral anterior nuclei of the thalamus. GP: globus pallidus (external and internal portions).  Pag. 9 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia Some of the fibres can exit from the external globus pallidus, they end up in the subthalamus. 4. Basal nuclei pathway In order to reach the corpus striatum the caudate, putamen and accumbens must be entered (neostriatum). Different cortical areas can originate the information, most of it derives from motor areas – primary motor cortex, supplementary motor cortex and premotor cortex. The fibres are sent simultaneously with those of the descending system. From the motor cortex 2 systems are obtained: one is descending and one is entering in the ‘check system’ to control the motor plan ideated by the cortex (being the basal ganglia). Some fibres are delivered from the sensory areas, similarly to the descending systems (1/3 of the pyramidal system). The primary somatosensory cortex as well as associative areas (such as the superior parietal lobule) deliver information to the striatum. The bundle of fibres formed from the cortex to the corpus striatum are referred to as the corticostriate fibres. Inside the corpus striatum some synapses occur, for the processing of the information. The ‘basal circuit’ consists in: the information from the cortex reach the neostriatum through the corticostriate fibres (putamen in the example below),  Pag. 10 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia exit to reach the globus pallidus internal to then reach the thalamus through the pallidofugal fibres. In the thalamus different nuclei can be entered, where different information arrive, for instance in the VA and VL the dento-thalamo- cortico part of the correlation system from the cerebellum arrive, the information are integrated and then fed back to the cortex. The main feedback is to the supplementary motor areas, also premotor and primary motor cortex can be reached, general this is a second passage, the first feedback is the supplementary and then the other regions are reached (premotor or primary). The feedback provides information for the motor act to provide information to the final common way through the pyramidal system. Corticostriate from different areas of the cortex -> neostriatum, process information -> inner globus pallidus -> thalamus -> feedback to the cortex. Generally the globus pallidus is active to inhibit the thalamus to maintain the signal at a certain level, when the motor act wants to be created the arrival of the information to the pallidus gives rise to the signal and the feeds back to the cortex. Other structures can be involved apart from those in the basal circuit. Subthalamus The subthalamus is a double way mainly connected to the globus pallidus external, some also to the globus pallidus internal. From the putamen (in the image) the globus pallidus external is reached, it then projects to the subthalamus and feeds back to the corpus striatum. Even though usually the exit to reach the thalamus is from the globus pallidus internal, to then reach the cortex. Substantia nigra Inputs are delivered in the pars reticulata of the substantia nigra from the putamen or the caudate, it processes the signal then from the pars compacta either feeds back to the corpus striatum or the continues and reaches the thalamus directly. There can therefore be a group of fibres exiting from the substantia nigra and entering the thalamus in the same areas converging to the ones that are exiting from the globus pallidus. These structures involved in the formation of complex circuits can also receive information directly from the cortex. 5. Global function of basal ganglia  Pag. 11 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia The cortex decides the motor act and sends it directly to the motoneurons in the spinal cord, to be able to have a fast execution of what is wanted. At the same time fibres carrying the same information are delivered to the basal ganglia to have a tight control. The basal ganglia have the role to prepare the function to perform correctly the motor act. From the basal ganglia, if an act wants to be performed, the continuous feedback to the cortex occurs in order to create something that has been selected as the correct sequence and recruitment – create the pattern to then be memorised (it is so known what a series of correct passages is to perform a given act). Given that a motor act is already memorised and it is already known how to be performed. Information is continuously delivered to the basal ganglia in order to check if what is being performed matches the pattern that is known should be performed in order to do the specific motor act. This control is performed on the same information that is contemporarily delivered to the descending systems to perform the motor act. If there is a new movement, there is the possibility to add the information from the basal ganglia and to intervene on the motor final common way, because before the activation of the motoneurons there is a pool of interneurons to modulate the new situation. There is the possibility to verify the synchronisation of the signal and see if what was good in another situation (in another motor act) could be applied to this new one too, this is why there is this integrated system one with the other. There is the delivery of the information from the cortex (motor and sensory) and other nuclei at the level of the brain (as it is seen in the schema) to the corpus striatum in order to have a check of the information, a feedback is then received to the structures where the information has originated. At the same time the information is delivered to the motor nuclei of the cranial nerves or on the anterior horn of the spinal cord, depending on which muscles are aimed. 6. Mechanisms of movement control Control of movement refers to the control of the motor act in order for it to be performed with accuracy and precision. There are different connections involved in motor control: From the cerebral cortex the information is delivered to aim the brainstem or the spinal cord. The brainstem receives information from the cortex, this ends up in different nuclei forming descending systems being part of the extrapyramidal ones, through these then the motoneurons of the spinal cord can be reached.  Pag. 12 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia Extrapyramidal tracts are important for example for posture. In the brainstem, among all the nuclei, are the vestibular ones, they receive information from the periphery and connect directly (independently) to the cerebellum. From the cerebral cortex circuits arriving at the basal ganglia. These are needed to provide accuracy to the motor control. The cerebral cortex delivers information to the basal ganglia, through the thalamus then it is fed back, during the elaboration in the basal ganglia what is wanted to be used for the planning of the motor act is chosen. In order to reach the thalamus the ansa reticularis (passing inferior to the subthalamus) or the fasciculus lenticularis (passing superiorly to the subthalamus) can be used; with the fasciculus is also possible to also synapse at the level of the subthalamus. Substantia nigra The substantia nigra can be entered from the corpus striatum, some fibres can enter the substantia nigra also directly from the cortex representing a minority. There is a reciprocal connection between the cortex and the substantia nigra forming the nigro-striatal and the striato-nigral fibres. Cerebellum acts as well in the system for control. It is not involved in the selection of what is needed in order to prepare the motor act, it allows to perform correctly the act thanks to the comparison it does between the information that is received directly from the cortex and that which is continuously delivered in abundance from the periphery (sensory information reaching the cerebellum). It checks that what was ideated to be performed from the cortex (information received from the cortex) is correspondent to that which is actually being performed (sensory information received). This is referred to as the sensory feedback. It allows to have the selection of the sequence of actions that can then be repeated with a low margin of errors. The sensory feedback is allowed thanks to the abundant afferents received by the cerebellum coming from the brainstem and the spinal cord. The main ones are the olivocerebellar and the spinocerebellar tracts, important information may also derive from the trigeminal, reticular and tecto (cerebellar) fibres. The cerebellum takes the information that the cortex has already planned and checked and then adds the last feature, being precision. The cerebellum and cortex communicate through the correlation system. From the cerebellum there is a feedback to the cortex; first there is the passage of the efferents are delivered to the thalamus, in the same nuclei that are reached from the basal ganglia, here the information is integrated and it is completely checked once arrived at the cortex. The dento- thalamo-cortical tract is so formed. 7. Internal capsule  Pag. 13 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia As per the image (2nd image), in a horizontal section, the anterior, genu and the posterior limbs of the internal capsule are seen. Additional limbs are present: the retrolentiform and the sublentiform limb, these are mainly devoted to the special senses ascending pathways (acoustic and auditory) and to the correlation system. (1st image) Visceral and somatic ascending pathways, somatic descending fibres and correlation system information pass through the internal capsule. A summary of all the information passing through the internal capsule. The fibres of the different systems pass through the limbs in specific regions, considering the different systems: Motor system: Pyramidal system - corticospinal tract passes in the posterior limb and the corticonuclear in the genu. Extrapyramidal system – they travel partly in the anterior and partly in the posterior limb. Correlation system (cerebellum). The cortico-ponto-cerebellar tracts (correlation system) pass in different limbs depending on which information: Turk’s bundle passes in the sublentiform limb. Fibres that correlate to the to the temporal lobe. Arnold’s bundle pass in the anterior limb. These are fibres that need to correlate with the frontal lobe. Parieto-occipital bundle passes in the posterior limb. Fibres that correlated to the parietal lobe. Fibres correlating to the occipital lobe pass through the retrolentiform limb. Ascending pathways. These are mainly passing in the posterior limb of the internal capsule except the information from the special senses, which are the acoustic reaching the sublentiform limb and the optic radiation reaching the retrolentiform. (Referring only to the image below-2nd) Retrolentiform limb The retrolentiform limb starts from the lateral geniculate body (metathalamus), from the posterior portion of the thalamus, therefore more posterior than the lentiform. The bundle of fibres move from medial to lateral, enter the internal capsule and rotate to move towards the calcarine fissure in an anteroposterior direction. The fibres following this course (and hence constituting the limb) are the optic radiation (geniculo-calcarine tract) and some being part of the correlation system between the cortex of the occipital lobe and the cerebellum. Sublentiform limb  Pag. 14 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia The sublentiform limb is a tract of the internal capsule originating from the medial geniculate body, from the posterior portion of the thalamus, the fibres move laterally to enter in the internal capsule and pass inferiorly to the lentiform (specifically the putamen) to be directed towards the temporal lobe. The name of the limb recalls the passage below the lentiform. In this limb the acoustic radiations, originating from the medial geniculate body, travel directed towards the primary auditory cortex located mainly in the superior gyrus of the temporal lobe. Some fibres of the correlation system passing through the limb to connect the cerebellum to the temporal lobe. The major limbs (posterior, anterior and genu) are involved in the other descending and ascending pathways. Anterior limb The anterior limb contains: Part of the correlation system needing to reach the frontal lobe, it is therefore important for the reverberant circuit of the cortex that goes mainly in the superior but also in the frontal thalamic radiation. Part of the extrapyramidal system, specifically those fibres that from the cortex then carry information to other nuclei of the brainstem (reticular formation, substantia nigra…) to then synapse and give rise to other descending tracts. Posterior limb The posterior limb is the largest one and is where the majority of the fibres pass through: The fibres composing the large superior thalamic radiation are found in the posterior limb, inside which the so-called superior lemniscus is present, being the sum of the trigeminal, medial, lateral and spinal lemniscus, hence the sum of all of them (being all inside the posterior limb of the internal capsule). These then project to the cortex using either the superior thalamic radiation (dots in the image) or the posterior thalamic radiation. The extrapyramidal system being directly connected to the cortex (not those synapsing with the tectum, reticular formation…) travel in the posterior limb, this represents the corticorubral, a very large tract descending close to the corticospinal. The corticospinal tract. The fibres that descend from the cortex need to pass through the internal capsule and further inferiorly through the cerebral peduncles. The somatotopism in the cortex is latero-medial cranio-caudal, this means that (for instance) the information from the face (cranial) is located very laterally in the cortex. When descending in the internal capsule, the information aimed to the cranial portion of the body move anteriorly, and then gradually more posteriorly in the internal capsule will be located the information for the caudal portion of the body. Therefore in the internal capsule a somatotopism for the motor system can be distinguished, being cranio-caudal antero-posterior. Close to the information destinated to the thoracic region (from the corticospinal) is the corticorubral tract, indeed the 2 of them (corticorubral and corticospinal) descend together until the thoracic portion, where the rubrospinal finishes. Information from other sources: The cerebral peduncles are the two stalks that attach the cerebrum to the brainstem. They are structures at the front of the midbrain which arise from the ventral pons and contain the large ascending (sensory) and descending (motor) nerve tracts that run to and from the cerebrum from the pons. Not to be confused with the cerebellar peduncles. https://en.wikipedia.org/wiki/Cerebral_peduncle Genu The genu contains the corticonuclear, that is a portion of the pyramidal system, it is located more anteriorly with respect to the corticospinal which is indeed more posterior. The information from the face (carried from the corticonuclear), following the somatotopism just described concerning the motor system, is located even more anteriorly with respect to all of the fibres carried by the corticospinal tract. A horizontal section  Pag. 15 a 15 International Medical School – FNC #13 – prof. Dellavia – basal ganglia Anterior, posterior and the inferior radiation. These are the part of the corona radiata that have to pass inside and are destinated to different lobes, these are all entering the tract. Here there is the passage that is indeed a corona radiata but there are some bundles connecting the lentiform and the caudate that oblige the fibres to deviate and group, there are therefore these peduncles/tracts of the thalamic radiation that are these projections grouped in this way, but this peduncles are conventional considering the typology of fibres. The fibres entering are seen.